This invention relates to a radiation thermometer and a radiation sensor with multiple sensor elements for detecting infrared radiation from differing regions, and to a method for determining a temperature by means of such a radiation thermometer or radiation sensor.
The art knows of radiation thermometers having just a single infrared sensor element disposed at the end of an optical waveguide. The waveguide ensures that only radiation from a predetermined solid angle range impinges on the sensor element. Thus, for example, the probe head of an infrared thermometer designed to take a patient""s temperature in the ear is dimensioned such that the sensor element exhibits a field of view only of the approximate size of the tympanic membrane. However, the field of view of the sensor element usually covers parts of both the tympanic membrane and the ear canal whose temperatures differ. Generally, therefore, not the tympanic temperature is taken, which is considered as being representative of the true body core temperature, but rather an intermediate value that lies between the tympanic and the ear canal temperature. Hence the accuracy of a temperature reading depends on the placement of the probe head in the ear canal, that is, on its distance to the tympanic membrane and on the angle it forms with the ear canal.
From WO 95/14913 an ear thermometer is known in which multiple sensor elements are arranged at the end of an optical waveguide so as to receive radiation from differing solid angle ranges. By corresponding evaluation of the signals supplied by the sensor elements, a temperature reading is obtainable which, while being relatively independent of the placement of the probe head in the ear, is likewise representative of an intermediate value which does not correspond to the true tympanic temperature.
The conventional infrared ear thermometers further have the disadvantage that the optical waveguide customarily employed, which is a small tube of a diameter of about 3 mm having its inner diameter gold plated, is very expensive, in addition to guiding heat from the ear into the interior of the probe head during a temperature measurement. Hence complex approaches are necessary to prevent corruption of the measurement result.
From EP 0 566 156 B1 an infrared sensor having two infrared sensitive elements is known, one being shielded against infrared radiation, the sensor being intended for use in a thermometer for measuring body temperature, and a method for manufacturing the sensor. By comparing the signals supplied by the two elements, a measurement signal is obtainable which is representative of the amount of incident infrared radiation and is largely free from electric noise and thermal disturbances. The infrared sensitive elements have their upper and undersides protected by coatings.
From JP-A-03-263001 an infrared sensor with a microlens is known, which is intended for use in an ear thermometer for taking a patient""s temperature, and a method for manufacturing the sensor. The microlens serves to focus the infrared radiation on the infrared sensor. It has a diameter of 1.44 mm, approximately.
The manufacture of the known infrared sensors is accomplished using the processes known from the manufacture of semi-conductors, involving the formation of a plurality of sensor elements on a substrate subsequently cut into individual sensors each having one element only which are then provided with an enclosure, etc.
From JP-A-03-248477 an infrared sensor having four identical infrared sensitive elements is known, which is intended for use in an ear thermometer for taking a patient""s temperature, and a method for manufacturing the sensor. The four elements are arranged on bridges extending across a recess in a substrate.
From JP-A-04-333292 a two-dimensional array of thermo-elements is known which is intended for an infrared image sensor.
From xe2x80x9cUncooled IR Focal Plane Arraysxe2x80x9d by Paul W. Kruse, SPIE, vol. 2552, pages 556-563, sensor arrays, that is, two-dimensional arrays of infrared sensor elements are known in which one sensor element is less than 0.1 mm long and wide.
It is an object of the present invention to provide a radiation thermometer of straightforward construction and a radiation sensor and a method of computing the temperature for a radiation thermometer which enables selective measurement of the temperature of objects filling only part of the field of view of the radiation thermometer.
This object is accomplished with a radiation thermometer having a radiation sensor with multiple infrared sensor elements and multiple optical elements, wherein a single optical element is associated with either only one sensor element or a group of sensors comprising multiple sensor elements. The optical elements operate to ensure that the sensor elements or sensor groups are able to receive only radiation that is emitted by a region defined within narrow limits. In this manner, the field of view of the radiation thermometer is split into a plurality of partial fields of view whose temperatures can be measured individually. For the purposes of an ear thermometer, a certain amount of overlap of the individual partial fields of view is tolerable.
Advantageous for use in an ear thermometer is an infrared multiple sensor, that is, an array of multiple sensor elements arranged on a common substrate, because with such a multiple sensor a sufficiently small thermometer probe head can be realized. The optical elements are preferably combined to form a single optical component (multiple optical system), advantageously forming an integrated optical component. In a particularly advantageous aspect, a radiation sensor of the present invention includes a multiple sensor and a multiple optical system which is arranged in close proximity to or on the surface of the multiple sensor. Radiation sensors of this type are known, for example, from U.S. Pat. No. 5,701,008, JP-A-57-142526, JP-A-1-47923 and DE 36 33 199 A1.
Preferably, however, the optical elements and the sensor elements are configured as an integrated electro-optical temperature sensor in which the optical elements, for example, are provided directly on the surface of the multiple sensor. Such a temperature sensor can be manufactured using the methods known from semiconductor manufacture. An electro-optical infrared sensor in which the individual sensor elements are heat sensitive capacitors is known from U.S. Pat. No. 5,631,467.
A method of the present invention for temperature determination by means of a radiation thermometer as, for example, an ear thermometer, that includes a radiation sensor comprising multiple sensor elements enables in particular the temperature to be taken in a patient""s ear, that is, the tympanic temperature to be measured, although the field of view of the radiation thermometer covers both parts of the tympanic membrane and parts of the ear canal. In such a case the sensor elements viewing the tympanic membrane will detect a higher temperature than the remaining sensor elements which view the ear canal. According to the present invention, the evaluation process uses only the temperature signals from those sensor elements that detect higher or significantly higher, or in other applications lower or significantly lower, temperatures than the remaining sensor elements.
In a particularly advantageous method, the process of temperature determination is preceded by a check to see whether the probe head of the thermometer is properly aligned in the ear canal. If it is not, that is, if the tympanic membrane is outside the field of view of the radiation sensor so that the probe head is directed at parts of the ear canal exclusively, all sensor elements will supply largely the same temperature values. Hence, when the evaluation of the temperature signals does not reveal a sufficiently appreciable temperature gradient within the field of view of the radiation sensor, the method of the present invention, rather than supplying a temperature measurement value, produces a corresponding error message or a request to repeat the measurement. In this embodiment of a thermometer of the present invention, it is necessary for the field of view of the radiation sensor to be greater than the diameter of the tympanic membrane so that also in cases where the probe head points directly at the tympanic membrane the surrounding ear canal is also covered, hence enabling the temperature gradient between the tympanic membrane and the ear canal to be identified.
A clinical thermometer operating according to the method of the present invention affords the advantage of obtaining excellent repeatability characteristics because the measured temperatures are largely independent of the respective placement of a probe head in the ear. According to the principle, namely, each measurement requires that only a single one or very few of a total of, for example, one hundred sensor elements view the tympanic membrane in order to be able to measure the tympanic temperature, that is, a potential fever condition, accurately.
Moreover, the structure of a radiation thermometer of the present invention is simplified in the use of a radiation sensor of the present invention because it obviates the need to provide as a waveguide a metal tube having its inside diameter gold plated as is otherwise customary, its functions being performed by the optical elements instead. Hence more possibilities are afforded in the design of the probe head of a radiation thermometer of the present invention because the radiation sensor may also be located directly at the end of the probe head, for example. Also, multiple radiation sensors arranged at relative inclinations may be provided at the end of the probe head in order to obtain a sufficiently wide field of view.
Embodiments of the present invention will be described in the following with reference to the accompanying drawing. Further embodiments are referred to in the description. In the drawing.